Method of making magnetic cores



- Patented .Feb. 22, 1927.

UN ITED STATES PATENT orl-"i cs.

WALT-HER EHLERS; 0F BERLIN-GRUNAU, GERMANY, ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK.

METHOD OF MAKING MAGNETIC COBES.

No Drawing. Application filed December 29, 1924, Serial No. 758,598, and in Germany January ,9,'1924. 1

My present invention relates to the manufacture of magnetic cores of pressed mag netic powder for induction coils and similar purposes.

l The object of my invention is to provide a method whereby the manufacture of such cores will be simplified andat the same time the space occupied by the cores may be utilized -to the best advantage.

l The cores of induction coils and similar apparatus are generally subdivided in order to avoid excessive current losse. They are made, for example, of sheet metal strips, wire or powder. lVhen wire or powder 1s used, the space occupied by the cores inmany cases is not utilized to the best advantage. It is possible to compress a mixture of powdered magnetic materia and in- '"sulatingmaterial in comparatively small volume by very high-pressure in the cold state. The use of presure high enough to press the mixture to the smallest possible practical volume may however be lnjurious to the magnetic material as well as result in poor insulation. The use of very high pressures is of conrseobiectionable from the standpoint of mechanical ClllllCUll'lOS involved in its production.

In carrying out my invention I avoid the use of very high pressures and at the same time secure better utilization of the space by applying heat to the mixture during the pressing operation. The results ob .tained by my method are made possible by the use of an insulating material. the properties of which are not ail'ected by the temperatures employed and which after cooling holds the grains of the magnetic material together securely and insulates them well electrically. The insulating material employed may be such that the temperature used in the pressing operatlon will remain solid. become plastic, or even liquid;

For comparatively low temperatures various varieties of glass may for example form a suitable insulating material. For higher temperatures porcelain or similar materials maybe employed which during the pressing operation will soften sufticiently to flow about-the particles of magnetic material. hen the temperature used in the pressing operation is so high that the magnetic material becomes plastic or liquid, it is advisable to use as an insulating'medium a material which is solid even at these high powdered magnetic material and dry insulating material andsimultaneously heating the mixture to a temperature at which one of the materials will soften.

3. The method of making a magnetic core which consists in pressing a mixture of powdered magnetic material and dry insulating material having a high fusing temperature and simultaneously heating the mixture to a temperature at which the magnetic material will soften and the insulating material will remain solid.

4. A magnetic core comprising a mixture of powdered magnetic material and dry brittle insulating material compressed into a stable t'orm. one of said materials having been heated during the pressing operation sufticiently to soften it and cause. it to flow around the particles of the other material and thereby reduce the size and number of the interstices between individual particles otthe mixture.

In witness whereof, I have hereunto setmy hand this 10th day of December, 1924.

WAL'lHER EHLERS.

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